1. Field of the Invention
The present invention relates generally to soldering and desoldering of SMD components, and more specifically to a heating device having a novel hot gas flow arrangement, nozzle attachment mechanism, and end nozzle design for soldering and desoldering solid state devices through utilization of a stream of hot neutral gas.
2. Description of the Prior Art
The subject of this patent is a heating head for soldering and de-soldering of SMD components using a hot neutral gas or air stream.
Numerous hot gas type soldering/desoldering machines are known for attaching and removing electronic components from a printed circuit board (PCB). One known solution is described by Polish Patent (# Ru-54524), in which a heating nozzle placed at the end of a heating device for dispersing a hot gas (air) is comprised of a round shroud in the form of a sliced cone. Situated in the shroud on one side is a threaded hole, while on the other side there is a round plate in which two or four narrow elongated holes are situated, distributed in parallel to the shape of the square or rectangle, in the case of 2 holes, or two parallel pairs perpendicular one to each other in the case of 4 holes, and in the middle there is one round hole. Discharge nozzles are fastened in the elongated holes, which are equipped with protruding directional flaps or end fittings. In the above solution, the discharge nozzles have a different construction applicable to a different type of solid state devices.
Also known are other designs of heater end nozzles or end fittings, in which the discharge nozzles have a conical shape, flattened at the bottom, made of thin wall tubing formed by a complicated multitask method of plastic forming coupled with thermal forming. In this type of end fittings, good parameters of working gas are achieved. However, due to the complicated production process, they are expensive. Furthermore, the above-described solution applies to only one element of a heating head. End nozzles have the same cross-section on their entire lengths. The shape of the shroud and the end nozzles has a direct effect on the parameters of the hot gas (air). In the previous solutions, there is too big a difference between the temperature of the hot gas in the middle and at both ends of the end nozzles.
There are also known other configurations of nozzles in which the end nozzles have a conical shape and are flattened at the ends. Such nozzles are made of a thin wall tubing formed by a compacted, multitasking forming process including hot forming. In such nozzles, the parameters of the hot gas for soldering are good, but because of the nature of the nozzle production process, they are also very expensive.
Another solution is known from Polish patent # Ru-54524, in which the electrical heater is comprised of a cylindrical ceramic shroud. Such shroud is enclosed on both ends with perforated end cups having centrally located holes to mount to the heater core in a shape of a cylinder with a centrally located hole and additional holes on the perimeters for electrical wires. The shroud, end cups and heater rod are made of an insulative material such as ceramics or quartz glass, and the shroud is inside the cylindrical thin wall tube made of an insulation material such as mica. The above solution concerns another element of the heating head, and is the predecessor of the solution presented in this application. This predecessor does not have characteristics concerning construction of the entire heating head.
There are also known solutions for complete heating heads. They are comprised of the handle, heater assembly, fast connecting mechanism, and nozzle. However, the parts of such prior heating heads make the usefulness of a complete head less practical and useful. For example, electrical supply and control wires and air lines are attached to the handle at the end of the handle along the axis of the heating head. This causes cumbersome cable pull sideways during hand held operations. In addition, the heater is placed inside the handle, which often causes overheating and shortens life of the device.
Reference is also made to the following prior art patents:
U.S. Pat. No. 4,295,596 issued to B. O. Doten et al. on Oct. 20, 1981, entitled xe2x80x9cMETHODS AND APPARATUS FOR BONDING AN ARTICLE TO A METALLIZED SUBSTRATE,xe2x80x9d discloses a hot gas type soldering/desoldering device wherein hot gas can be directed substantially parallel to the surface of a printed circuit board by angled deflectors on the end of the heater nozzle. Doten et al. is illustrative of the fact that many early prior art nozzles were held to the heater body by bolts and therefore could not be quickly attached or removed therefrom.
U.S. Pat. No. 4,564,135 issued to A. J. Barresi et al. on Jan. 14, 1986, entitled xe2x80x9cCHIP CARRIER SOLDERING TOOL,xe2x80x9d discloses a nozzle for soldering/desoldering electronic components which diverts most of the hot gas flow to the periphery of the component, although not in the same manner as the present invention.
U.S. Pat. No. 4,767,047 issued to R. I. Todd et al. on Aug. 30, 1988, entitled xe2x80x9cDESOLDERING DEVICE,xe2x80x9d discloses a hot gas type desoldering device having a suction device for lifting a circuit from a circuit board. However, such solution discloses none of the specific improvements of the present invention.
U.S. Pat. No. 4,787,548 issued to L. A. Abbagnaro et al. on Nov. 29, 1988, entitled xe2x80x9cNOZZLE STRUCTURE FOR SOLDERING AND DESOLDERING,xe2x80x9d discloses an adjustably positionable nozzle for a soldering/desoldering tool having a means for uniformly distributing heated air through the nozzle. However, such reference teaches a different nozzle structure, and the nozzles are attached to the soldering device by holes or bores which receive screws, which task is time consuming and inconvenient. Also see U.S. Pat. Nos. 4,899,920 and 4,972,990 issued to Abagnaro et al.
U.S. Pat. No. 4,805,827 issued to B. W. Coffman et al. on Feb. 21, 1989, entitled xe2x80x9cMETHOD OF SOLDERING WITH HEATED FLUID AND DEVICE THEREFOR,xe2x80x9d discloses a nozzle for a hot gas soldering device having a horizontal baffle member which directs the gas laterally to the sides of the nozzle, and then downwardly to the sides of an electronic component. While laterally deflecting the gas while in the nozzle apparently mixes the air so that when it is directed across the component it has a more uniform temperature, such solution does not increase the uniformity of the gas flow from the heater head through the nozzle and across the electronic component as in the present system.
U.S. Pat. No. 4,858,820 issued to G. M. Kent on Aug. 22, 1989, entitled xe2x80x9cDESOLDERING AID AND METHOD,xe2x80x9d discloses a cap-like nozzle desoldering attachment. The Kent nozzle is primarily designed to desolder older electronic components wherein the leads extend from the sides of the component, rather than the more modern BGA type components.
U.S. Pat. No. 5,380,982 issued to W. S. Fortune on Jan. 10, 1995, entitled xe2x80x9cMETALLIC CONDUCTIONxe2x80x94HOT GAS SOLDERINGxe2x80x94DESOLDERING SYSTEM,xe2x80x9d discloses a hot air type system which can be used with a tip designed for desoldering an SMD device. However, Fortune does not teach a suction cup on the end of the vacuum tube or a nozzle structure for uniformly distributing such hot air.
U.S. Pat. No. 5,419,481 issued to C. S. Lasto et al. on May 30, 1995, entitled xe2x80x9cPROCESS AND APPARATUS FOR ATTACHING/DETACHING LAND GRID ARRAY COMPONENTS,xe2x80x9d discloses another soldering/desoldering nozzle for BGA, as well as SGA and CGA type electronic components. While the gas flow inlet and exhaust flow patterns created by the nozzle result in a continuous flow and apparently more uniform solder melting, Lasto et al. does not attempt to provide a more uniform flow through the heater head as in the present invention.
U.S. Pat. No. 5,579,979 issued to G. Kurpiela on Dec. 3, 1996, entitled xe2x80x9cSOLDERING/DESOLDERING NOZZLES FOP SMD""S,xe2x80x9d discloses an improved heating nozzle having slotlike recesses along its bottom periphery through which hot gas is directed at the leads of an electronic component. Such nozzle includes vent holes to allow for circulation of the has gas across the leads; however, such vent holes are situated on the corners of the nozzle rather than slightly spaced from the corners as in the present inventor""s arrangement.
U.S. Pat. No. 5,785,237 issued to C. S. Lasto et al. on Jul. 28, 1998, entitled xe2x80x9cDIFFERENTIAL MULTI-FLOW CONTROL NOZZLES APPARATUS AND PROCESS,xe2x80x9d discloses an improved hot gas-type nozzle which apparently allows for more uniform heating and decreases the reflow cycle time by directing the entire gas flow against the top surface of the leads, causing heat to conduct through the leads and melt the solder on the underside of the component.
U.S. Pat. No. 5,890,646 issued to A. Q. Tang et al. on Apr. 6, 1999, entitled xe2x80x9cSOLDERING/DESOLDERING APPARATUS WITH SPRING-LOADED FLOATING VACUUM PICKUP DEVICE,xe2x80x9d discloses a soldering/desoldering apparatus having a vacuum pickup connected to a spring-loaded control on the handle of the apparatus. Manual pressure on a slide rod allows the height of the pickup tube and suction device to pick up and remove components during desoldering, although the spring-loaded control differs from the present vacuum tube control system, which is not spring loaded.
U.S. Pat. No. 6,059,170 issued to L. J. Jimarez on May 9, 2000, entitled xe2x80x9cMETHOD AND APPARATUS FOR INSULATING MOISTURE SENSITIVE PBGA""S,xe2x80x9d discloses a soldering/desoldering device wherein a temperature shield covers the electronic component during soldering/desoldering, particularly for plastic ball grid array (PBGA) devices. While Jimarez teaches a state-of-the-art nozzle, such nozzle does not disclose any of the major features of the present invention.
U.S. Pat. No. 6,105,847 issued to Y. Kim on Aug. 22, 2000, entitled xe2x80x9cNOZZLE STRUCTURE OF REPAIR APPARATUS FOR SEMICONDUCTOR PACKAGE,xe2x80x9d teaches another nozzle solution for a desoldering device, the main difference from prior nozzles being that the exhaust flow is better directed upwardly away from adjacent electronic components.
U.S. Pat. No. 6,131,791 issued to H. Masaki on Oct. 17, 2000, entitled xe2x80x9cSOLDERING AND DESOLDERING DEVICE WITH IMPROVED PICKUP DEVICE,xe2x80x9d discloses a handheld hot gas soldering/desoldering device having a vacuum pickup tube adjustment control on the handpiece portion of the device for raising and lowering the vacuum pickup tube. The Masaki vacuum tube control also includes a spring to absorb excess force on the knob which might damage the electronic component being moved or held, while the present system does not include any such spring mechanism.
U.S. Pat. No. 6,182,884 issued to W. M. Ma et al. on Feb. 6, 2001, entitled xe2x80x9cMETHOD AND APPARATUS FOR REWORKING CERAMIC BALL GRID ARRAY ON CERAMIC COLUMN GRID ARRAY ON CIRCUIT CARDS,xe2x80x9d discloses an improved nozzle for a soldering/desoldering device having a resilient member affixed to a support member upon which an electronic component rests. The component presses against the resilient member during soldering so that the lower portion of the solder ball array is situated slightly below the lower end of the nozzle, so that when the chip is placed on the circuit board the resilient means exerts a downward pressure on the chip so that it is evenly secured to the board even if the board is slightly warped.
U.S. Pat. No. 6,196,439 issued to A. T. Mays et al. on Mar. 6, 2001, entitled xe2x80x9cMETHOD AND APPARATUS FOR uBGA REMOVAL AND REATTACH,xe2x80x9d discloses a soldering/desoldering device nozzle and apparatus wherein heat is provided via conduction of heat through the electronic device rather than through convection of gas.
U.S. Pat. No. 6,220,503 issued to W. L. Cox et al. on Apr. 24, 2001, entitled xe2x80x9cREWORK AND UNDERFILL NOZZLE FOR ELECTRONIC COMPONENTS,xe2x80x9d discloses a desoldering nozzle having an outer tube that provides a gas tight seal around the electronic component, an inner shaft attached to the outer tube by baffles, forming ducts, and a water vapor port. Such water vapor is apparently added to the gas to increase its overall heat capacity. A reversing valve is also used to control the direction of flow of gas and water vapor, thereby providing more uniform heating or reflowing of the solder ball connections.
U.S. Pat. No. 6,223,968 issued to C. F. Gabriel et al. on May 1, 2001, entitled xe2x80x9cSOLDER BONDING/DEBONDING NOZZLE INSERT,xe2x80x9d discloses a nozzle having an insert attached to its lower end that allows the size of the bottom opening to be adjusted, with different inserts fitting different sizes of components. While one using the Gabriel arrangement does not have to have switch to a completely different nozzle structure for each different electronic component, such arrangement is not similar to the present inventor""s nozzle structure.
U.S. Pat. No. 6,257,478 issued to J. Straub on Jul. 10, 2001, entitled xe2x80x9cSOLDERING/UNSOLDERING ARRANGEMENT,xe2x80x9d discloses a soldering/desoldering device having a xe2x80x9cbell-shapedxe2x80x9d nozzle such that heated gas flows downwardly through spaces around the edge of the nozzle and across the electronic component, and then exits upwardly into the nozzle through exhaust valves or ports. A heat distribution plate allows heat to radiate downwardly and more uniformly onto the electronic component than in previous designs.
While each of such solutions has its own advantages and uses, the prior art does not teach a heater wherein hot gas is passed uniformly both across the heating element and through the heating nozzles as in the present system, which results in a much smaller difference in temperature of the hot gas in different areas of the nozzle, and therefore results in more uniform heating and soldering/desoldering of electronic components. In addition, manufacture of the present system is more economical and efficient than previous solutions.
The present heating head is comprised generally of a handle portion, heater assembly, nozzle connecting mechanism, and heater nozzle. On the upper end of the handle there is an oval like surface angled with respect to the axis of the handle. The handle housing is made in two halves of high temperature thermoset, anti-static plastic having a groove and matching tongue, i.e. clam style housing. Situated on the angled surface there are inlets for gas and electrical connections via an anti-static, multi-wire, flexible cable inside of which there are wires of different gauges. The gas supply is supplied through an anti-static silicon tubing, while also included is a small diameter vacuum line. Inside the handle is a mechanism for laterally moving a metal vacuum tube, which tube extends through the heater sub-assembly and heating nozzle. Attached to the lower end of the metal vacuum tube is a vacuum cup made conveniently from high temperature silicon. The vacuum cup is in the shape of a caved-in dome with a central hole in which a stopping ring/washer is molded, thereby preventing the vacuum tube from inadvertently protruding through the vacuum cup.
The heater sub-assembly is held to the handle via an insulation ring, which also limits heat transfer to the handle. The lower end of the handle to which the heater sub-assembly is attached has a protective, perforated shroud with elongated ventilation holes. The heater sub-assembly is comprised of a thin wall metal tubing shroud having a pair of outwardly protruding press-outs close to its lower end and having a perforated end cup over the same end. Located just inside the shroud is an insulative (artificial mica) tube, while just inside said insulative tube is another high temperature insulative tube (quartz glass or ceramic). Inside the second insulative tube there is a resistive heater which is wound on a ceramic core in the shape of a cylinder and having elongated bosses on its perimeter along the axis. The ceramic core also has an undercut at the end closest to the perforated shroud end cup, with one or two thermocouples for sensing the temperature of the hot air or gas placed in such undercut. On the elongated bosses there is wound a heating element. Behind the heating coil there is a flow equalizer made of ceramic tubing, which equalizes the flow of gas through the heater assembly. At the back of the heating core there is another thermocouple for sensing the temperature along the back of the heater. A grounding wire is permanently attached on the inner side of the metal heater shroud.
A mechanism for quickly connecting and disconnecting a heater nozzle to the heater head is additionally provided. Such mechanism is comprised of a cylindrical shroud with two press-in""s corresponding to the press outs on the heater shroud, which is slid over the end of the heater shroud. A perpendicular bar with a threaded hole or PEM-nut and a screw to secure the cylindrical part of the connecting mechanism to the heater shroud via a tong cut in such cylindrical part is spot welded (glued or brazed) to the outer surface of such cylinder. Below on the cylindrical part of the quick change connecting mechanism is an outside mechanism cover, which is cylindrical at the bottom and conical at the top. Attached to the lower portion of the cover is an upper ring having a minimum of two and up to four wings, each of said wings having upwardly facing indents in them. Located inside the mechanism cover is a flanged moving ring which is slid over the cylindrical part of the quick connecting mechanism. Such moving flanged ring is pressed against the wings by the force of a high temperature spring preferably made out of a highest grade high temperature steel alloy.
The wings of the upper ring of the quick connecting mechanism are matched with similar wings on the heating nozzles. In one embodiment, each heating nozzle is generally comprised of a chamber disposed at the end of a connecting cylinder. Such chamber has the shape of a truncated pyramid with a square bottom cover. Centrally located on such bottom cover is a round hole through which the metal vacuum tube protrudes, as well as usually two or four symmetrically located (versus the central hole) rectangular openings in which there are placed end nozzles made conveniently out of bent, thin, stainless steel sheet metal. Such end nozzles are generally wider at the end protruding out of the bottom of the truncated pyramid and narrower at the end nozzle ends. The inner walls of the end nozzles are parallel to the nozzle axis and have a preformed overlap. However, the outer walls of the end nozzles are not parallel to the axis of the nozzle, and are generally angled inward. In addition, such outer walls are also longer than other end nozzle walls. The longer parts are either straight or bent outwards to direct the air flow as required. In another embodiment, the end nozzles are generally in the shape of a rectangular box or chamber, the dimensions of which depend on the type of SMT device. The box is created by folding a thin sheet metal cut out. Circulation holes are centrally located on each side wall, while circulation cut-ins are located along the bottom edge of the each side wall near the corners of the chamber.